Field of the Invention
The present invention relates to a superconductor wire subjected to insulation coating and a superconducting coil.
Description of the Related Art
A metal-based superconductor wire formed of a material such as NbTi, which has been conventionally used, is provided in the form of a round wire, a rectangular wire, or the like. Accordingly, the degree of freedom of the shape is high. In contrast, in a high-temperature oxide superconductor wire having a critical temperature of approximately 90 to 100K, which is formed of a Bi-based or Y-based material, a superconductor layer is formed of a ceramic and the wire structure has a tape shape. Accordingly, mechanical characteristics, such as bending and twisting, are likely to deteriorate.
For example, as shown in FIG. 4, a superconductor wire 100 formed of a Bi-based material is manufactured in a structure, in which a superconductor layer 101 formed of a Bi-based material is covered with a sheath member 102 formed of Ag, using a powder in tube method (PIT method) or the like. On the other hand, the structure of a rare earth element-based (for example, Y) superconductor wire 200 is completely different as for example shown in FIG. 5.
In the superconductor wire 200 shown in FIG. 5, an oxide superconductor layer 203 is laminated on a tape-shaped metal substrate 201 with an intermediate layer 202 interposed therebetween using a deposition method, and stabilization layers 204 and 205, mode of, for example, Ag and Cu, are laminated thereon. Therefore, unlike in the case of designing a superconducting coil using a wire having a symmetrical structure in the thickness direction as in the Bi-based superconductor wire 100 shown in FIG. 4, in order to form a superconducting coil using the rare earth element-based superconductor wire 200, it is necessary to design the superconducting coil taking directivity, such as bending and twisting, in consideration.
In order to wind a tape-shaped superconductor wire to form a coil, it is necessary to cover the superconductor wire with an insulating material in order to ensure electrical insulation between superconductor wires.
As methods of insulation-coating the superconductor wire, a method of winding a resin tape, such as a polyimide tape, on the outer periphery of a tape-shaped superconductor wire and a method of forming a resin coating on the outer peripheral surface of the superconductor wire by applying a resin on the outer peripheral surface of the superconductor wire and baking the resin (refer to Japanese Unexamined Patent Application, First Publication No. 2000-311526) are known.
The technique described in Japanese Unexamined Patent Application, First Publication No. 2000-311526 is a technique applied to a Bi-based superconductor wire that is formed using the PIT method of filling material powder of the oxide superconductor into a metal tube and performing diameter reduction processing. The Bi-based superconductor wire formed by the PIT method has an elliptical cross-sectional shape as shown in FIG. 4, and a resin coating can be formed by applying a resin to the entire outer periphery of the superconductor wire and baking the resin.
In contrast, the rare earth element-based superconductor wire 200 shown in FIG. 5 has a rectangular cross-sectional shape and four corners that are angular. Therefore, in order to perform insulation coating on the superconductor wire 200, a method of forming an insulation coating by winding insulating tapes, such as polyimide tapes, so as to overlap each other or a method of forming an insulation coating by applying a thick resin layer on the outer peripheral surface and baking the resin layer has been studied.
In the superconducting coil impregnated with resin, peeling stress is applied in the vertical direction of the superconductor wire 200 during the cooling of the superconducting coil due to a difference in thermal expansion between the epoxy resin, which is an impregnating material, and the metal substrate 201 and the stabilization layer 205 formed of Cu that form the superconductor wire 200 or due to shrinkage when non-linear thermal expansion at low temperatures is taken into consideration. Accordingly, there is a possibility that the superconductor wire will deteriorate.
In addition, when performing the impregnation of epoxy resin, a process of making the epoxy resin spread out up to all corners of the coil using a vacuum impregnation method is performed. On the other hand, when resin impregnation is performed using a method other than the vacuum impregnation method, the mechanical strength (coil stiffness) of the superconducting coil may be reduced. Therefore, it is considered that the vacuum impregnation method is the most desirable.
Incidentally, when a superconducting coil is formed using a superconductor wire that is insulation-coated and the superconducting coil is impregnated with resin using a vacuum impregnation method or the like, a peeling force is applied in the vertical direction of the superconductor wire 200 due to the thermal expansion difference as described above. In the rare earth element-based superconductor wire 200 in which a number of layers are laminated as described above, there have been cases where the strength opposing the peeling stress decreases.
For example, in the case of a structure in which the intermediate layer 202, the oxide superconductor layer 203, and the stabilization layers 204 and 205 are laminated on the metal substrate 201, there is a possibility that a part of the intermediate layer 202 or the superconductor layer 203 will be peeled off due to the action of the peeling stress described above.
The present invention has been made in view of such a situation in the related art, and it is an object of the present invention to provide a superconductor wire having a laminated structure in which peeling does not occur in a part of each of an intermediate layer and a superconductor layer even if peeling stress is applied due to coil processing.